/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:	    arm_fir_decimate_f32.c
*
* Description:	FIR decimation for floating-point sequences.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated
*
* Version 0.0.7  2010/06/10
*    Misra-C changes done
*
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @defgroup FIR_decimate Finite Impulse Response (FIR) Decimator
 *
 * These functions combine an FIR filter together with a decimator.
 * They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion.
 * Conceptually, the functions are equivalent to the block diagram below:
 * \image html FIRDecimator.gif "Components included in the FIR Decimator functions"
 * When decimating by a factor of <code>M</code>, the signal should be prefiltered by a lowpass filter with a normalized
 * cutoff frequency of <code>1/M</code> in order to prevent aliasing distortion.
 * The user of the function is responsible for providing the filter coefficients.
 *
 * The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner.
 * Instead of calculating all of the FIR filter outputs and discarding <code>M-1</code> out of every <code>M</code>, only the
 * samples output by the decimator are computed.
 * The functions operate on blocks of input and output data.
 * <code>pSrc</code> points to an array of <code>blockSize</code> input values and
 * <code>pDst</code> points to an array of <code>blockSize/M</code> output values.
 * In order to have an integer number of output samples <code>blockSize</code>
 * must always be a multiple of the decimation factor <code>M</code>.
 *
 * The library provides separate functions for Q15, Q31 and floating-point data types.
 *
 * \par Algorithm:
 * The FIR portion of the algorithm uses the standard form filter:
 * <pre>
 *    y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]
 * </pre>
 * where, <code>b[n]</code> are the filter coefficients.
 * \par
 * The <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>.
 * Coefficients are stored in time reversed order.
 * \par
 * <pre>
 *    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
 * </pre>
 * \par
 * <code>pState</code> points to a state array of size <code>numTaps + blockSize - 1</code>.
 * Samples in the state buffer are stored in the order:
 * \par
 * <pre>
 *    {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}
 * </pre>
 * The state variables are updated after each block of data is processed, the coefficients are untouched.
 *
 * \par Instance Structure
 * The coefficients and state variables for a filter are stored together in an instance data structure.
 * A separate instance structure must be defined for each filter.
 * Coefficient arrays may be shared among several instances while state variable array should be allocated separately.
 * There are separate instance structure declarations for each of the 3 supported data types.
 *
 * \par Initialization Functions
 * There is also an associated initialization function for each data type.
 * The initialization function performs the following operations:
 * - Sets the values of the internal structure fields.
 * - Zeros out the values in the state buffer.
 * - Checks to make sure that the size of the input is a multiple of the decimation factor.
 *
 * \par
 * Use of the initialization function is optional.
 * However, if the initialization function is used, then the instance structure cannot be placed into a const data section.
 * To place an instance structure into a const data section, the instance structure must be manually initialized.
 * The code below statically initializes each of the 3 different data type filter instance structures
 * <pre>
 *arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState};
 *arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};
 *arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};
 * </pre>
 * where <code>M</code> is the decimation factor; <code>numTaps</code> is the number of filter coefficients in the filter;
 * <code>pCoeffs</code> is the address of the coefficient buffer;
 * <code>pState</code> is the address of the state buffer.
 * Be sure to set the values in the state buffer to zeros when doing static initialization.
 *
 * \par Fixed-Point Behavior
 * Care must be taken when using the fixed-point versions of the FIR decimate filter functions.
 * In particular, the overflow and saturation behavior of the accumulator used in each function must be considered.
 * Refer to the function specific documentation below for usage guidelines.
 */

/**
 * @addtogroup FIR_decimate
 * @{
 */

/**
 * @brief Processing function for the floating-point FIR decimator.
 * @param[in] *S        points to an instance of the floating-point FIR decimator structure.
 * @param[in] *pSrc     points to the block of input data.
 * @param[out] *pDst    points to the block of output data.
 * @param[in] blockSize number of input samples to process per call.
 * @return none.
 */

void arm_fir_decimate_f32(
    const arm_fir_decimate_instance_f32* S,
    float32_t* pSrc,
    float32_t* pDst,
    uint32_t blockSize)
{
	float32_t* pState = S->pState;                 /* State pointer */
	float32_t* pCoeffs = S->pCoeffs;               /* Coefficient pointer */
	float32_t* pStateCurnt;                        /* Points to the current sample of the state */
	float32_t* px, *pb;                            /* Temporary pointers for state and coefficient buffers */
	float32_t sum0;                                /* Accumulator */
	float32_t x0, c0;                              /* Temporary variables to hold state and coefficient values */
	uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
	uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M;  /* Loop counters */

#ifndef ARM_MATH_CM0

	uint32_t blkCntN4;
	float32_t* px0, *px1, *px2, *px3;
	float32_t acc0, acc1, acc2, acc3;
	float32_t x1, x2, x3;

	/* Run the below code for Cortex-M4 and Cortex-M3 */

	/* S->pState buffer contains previous frame (numTaps - 1) samples */
	/* pStateCurnt points to the location where the new input data should be written */
	pStateCurnt = S->pState + (numTaps - 1u);

	/* Total number of output samples to be computed */
	blkCnt = outBlockSize / 4;
	blkCntN4 = outBlockSize - (4 * blkCnt);

	while(blkCnt > 0u) {
		/* Copy 4 * decimation factor number of new input samples into the state buffer */
		i = 4 * S->M;

		do {
			*pStateCurnt++ = *pSrc++;

		} while(--i);

		/* Set accumulators to zero */
		acc0 = 0.0f;
		acc1 = 0.0f;
		acc2 = 0.0f;
		acc3 = 0.0f;

		/* Initialize state pointer for all the samples */
		px0 = pState;
		px1 = pState + S->M;
		px2 = pState + 2 * S->M;
		px3 = pState + 3 * S->M;

		/* Initialize coeff pointer */
		pb = pCoeffs;

		/* Loop unrolling.  Process 4 taps at a time. */
		tapCnt = numTaps >> 2;

		/* Loop over the number of taps.  Unroll by a factor of 4.
		 ** Repeat until we've computed numTaps-4 coefficients. */

		while(tapCnt > 0u) {
			/* Read the b[numTaps-1] coefficient */
			c0 = *(pb++);

			/* Read x[n-numTaps-1] sample for acc0 */
			x0 = *(px0++);
			/* Read x[n-numTaps-1] sample for acc1 */
			x1 = *(px1++);
			/* Read x[n-numTaps-1] sample for acc2 */
			x2 = *(px2++);
			/* Read x[n-numTaps-1] sample for acc3 */
			x3 = *(px3++);

			/* Perform the multiply-accumulate */
			acc0 += x0 * c0;
			acc1 += x1 * c0;
			acc2 += x2 * c0;
			acc3 += x3 * c0;

			/* Read the b[numTaps-2] coefficient */
			c0 = *(pb++);

			/* Read x[n-numTaps-2] sample for acc0, acc1, acc2, acc3 */
			x0 = *(px0++);
			x1 = *(px1++);
			x2 = *(px2++);
			x3 = *(px3++);

			/* Perform the multiply-accumulate */
			acc0 += x0 * c0;
			acc1 += x1 * c0;
			acc2 += x2 * c0;
			acc3 += x3 * c0;

			/* Read the b[numTaps-3] coefficient */
			c0 = *(pb++);

			/* Read x[n-numTaps-3] sample acc0, acc1, acc2, acc3 */
			x0 = *(px0++);
			x1 = *(px1++);
			x2 = *(px2++);
			x3 = *(px3++);

			/* Perform the multiply-accumulate */
			acc0 += x0 * c0;
			acc1 += x1 * c0;
			acc2 += x2 * c0;
			acc3 += x3 * c0;

			/* Read the b[numTaps-4] coefficient */
			c0 = *(pb++);

			/* Read x[n-numTaps-4] sample acc0, acc1, acc2, acc3 */
			x0 = *(px0++);
			x1 = *(px1++);
			x2 = *(px2++);
			x3 = *(px3++);

			/* Perform the multiply-accumulate */
			acc0 += x0 * c0;
			acc1 += x1 * c0;
			acc2 += x2 * c0;
			acc3 += x3 * c0;

			/* Decrement the loop counter */
			tapCnt--;
		}

		/* If the filter length is not a multiple of 4, compute the remaining filter taps */
		tapCnt = numTaps % 0x4u;

		while(tapCnt > 0u) {
			/* Read coefficients */
			c0 = *(pb++);

			/* Fetch  state variables for acc0, acc1, acc2, acc3 */
			x0 = *(px0++);
			x1 = *(px1++);
			x2 = *(px2++);
			x3 = *(px3++);

			/* Perform the multiply-accumulate */
			acc0 += x0 * c0;
			acc1 += x1 * c0;
			acc2 += x2 * c0;
			acc3 += x3 * c0;

			/* Decrement the loop counter */
			tapCnt--;
		}

		/* Advance the state pointer by the decimation factor
		 * to process the next group of decimation factor number samples */
		pState = pState + 4 * S->M;

		/* The result is in the accumulator, store in the destination buffer. */
		*pDst++ = acc0;
		*pDst++ = acc1;
		*pDst++ = acc2;
		*pDst++ = acc3;

		/* Decrement the loop counter */
		blkCnt--;
	}

	while(blkCntN4 > 0u) {
		/* Copy decimation factor number of new input samples into the state buffer */
		i = S->M;

		do {
			*pStateCurnt++ = *pSrc++;

		} while(--i);

		/* Set accumulator to zero */
		sum0 = 0.0f;

		/* Initialize state pointer */
		px = pState;

		/* Initialize coeff pointer */
		pb = pCoeffs;

		/* Loop unrolling.  Process 4 taps at a time. */
		tapCnt = numTaps >> 2;

		/* Loop over the number of taps.  Unroll by a factor of 4.
		 ** Repeat until we've computed numTaps-4 coefficients. */
		while(tapCnt > 0u) {
			/* Read the b[numTaps-1] coefficient */
			c0 = *(pb++);

			/* Read x[n-numTaps-1] sample */
			x0 = *(px++);

			/* Perform the multiply-accumulate */
			sum0 += x0 * c0;

			/* Read the b[numTaps-2] coefficient */
			c0 = *(pb++);

			/* Read x[n-numTaps-2] sample */
			x0 = *(px++);

			/* Perform the multiply-accumulate */
			sum0 += x0 * c0;

			/* Read the b[numTaps-3] coefficient */
			c0 = *(pb++);

			/* Read x[n-numTaps-3] sample */
			x0 = *(px++);

			/* Perform the multiply-accumulate */
			sum0 += x0 * c0;

			/* Read the b[numTaps-4] coefficient */
			c0 = *(pb++);

			/* Read x[n-numTaps-4] sample */
			x0 = *(px++);

			/* Perform the multiply-accumulate */
			sum0 += x0 * c0;

			/* Decrement the loop counter */
			tapCnt--;
		}

		/* If the filter length is not a multiple of 4, compute the remaining filter taps */
		tapCnt = numTaps % 0x4u;

		while(tapCnt > 0u) {
			/* Read coefficients */
			c0 = *(pb++);

			/* Fetch 1 state variable */
			x0 = *(px++);

			/* Perform the multiply-accumulate */
			sum0 += x0 * c0;

			/* Decrement the loop counter */
			tapCnt--;
		}

		/* Advance the state pointer by the decimation factor
		 * to process the next group of decimation factor number samples */
		pState = pState + S->M;

		/* The result is in the accumulator, store in the destination buffer. */
		*pDst++ = sum0;

		/* Decrement the loop counter */
		blkCntN4--;
	}

	/* Processing is complete.
	 ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
	 ** This prepares the state buffer for the next function call. */

	/* Points to the start of the state buffer */
	pStateCurnt = S->pState;

	i = (numTaps - 1u) >> 2;

	/* copy data */
	while(i > 0u) {
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		i--;
	}

	i = (numTaps - 1u) % 0x04u;

	/* copy data */
	while(i > 0u) {
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		i--;
	}

#else

	/* Run the below code for Cortex-M0 */

	/* S->pState buffer contains previous frame (numTaps - 1) samples */
	/* pStateCurnt points to the location where the new input data should be written */
	pStateCurnt = S->pState + (numTaps - 1u);

	/* Total number of output samples to be computed */
	blkCnt = outBlockSize;

	while(blkCnt > 0u) {
		/* Copy decimation factor number of new input samples into the state buffer */
		i = S->M;

		do {
			*pStateCurnt++ = *pSrc++;

		} while(--i);

		/* Set accumulator to zero */
		sum0 = 0.0f;

		/* Initialize state pointer */
		px = pState;

		/* Initialize coeff pointer */
		pb = pCoeffs;

		tapCnt = numTaps;

		while(tapCnt > 0u) {
			/* Read coefficients */
			c0 = *pb++;

			/* Fetch 1 state variable */
			x0 = *px++;

			/* Perform the multiply-accumulate */
			sum0 += x0 * c0;

			/* Decrement the loop counter */
			tapCnt--;
		}

		/* Advance the state pointer by the decimation factor
		 * to process the next group of decimation factor number samples */
		pState = pState + S->M;

		/* The result is in the accumulator, store in the destination buffer. */
		*pDst++ = sum0;

		/* Decrement the loop counter */
		blkCnt--;
	}

	/* Processing is complete.
	 ** Now copy the last numTaps - 1 samples to the start of the state buffer.
	 ** This prepares the state buffer for the next function call. */

	/* Points to the start of the state buffer */
	pStateCurnt = S->pState;

	/* Copy numTaps number of values */
	i = (numTaps - 1u);

	/* copy data */
	while(i > 0u) {
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		i--;
	}

#endif /*   #ifndef ARM_MATH_CM0        */

}

/**
 * @} end of FIR_decimate group
 */
